Personal mobile communication (PMC) devices such as smart phones are becoming increasingly ubiquitous. Such devices may be capable of accessing voice and/or data services operating within various communication bands. For example, it is not unusual for a modern PMC device to include two-way voice communication across a mobile carrier radio link; two-way Internet access via the mobile carrier radio link; 802.11 data communication with an 802.11 access point, with an 802.11-enabled computer, and/or with another 802.11-enabled PMC device; a Bluetooth® radio link, a global positioning system (GPS) receiver, etc. Multiple radio frequency (RF) receivers associated with these diverse communication services may be required to operate simultaneously and in close proximity on small circuit boards within a PMC device.
Additional information regarding the IEEE 802.11 standard may be found in ANSI/IEEE Std. 802.11, Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications (published 1999; reaffirmed June 2003). Additional information regarding Bluetooth® may be found in 802.15.3c-2009 IEEE Standard for Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements. Part 15.3: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for High Rate Wireless Personal Area Networks (WPANs) Amendment 2: Millimeter-wave-based Alternative Physical Layer Extension.
This situation poses challenges for receiver design in various ways. For example, transmitted signals create strong RF fields which must be filtered by the receivers. In addition, local oscillators (LOs) associated with the receivers themselves can create spurious harmonics (“spurs”) of substantial magnitude. Spurs may be generated as unwanted byproducts of mixing and other frequency conversion operations used to convert a base oscillator signal to the required LO frequency.
RF energy from spurs may overlap frequencies within radio bands associated with other co-located receivers, as described above. To alleviate this type of interference, costs may be incurred and circuit board space sacrificed as filters and/or shielding are added at the offending LO and/or at receiver front-ends impacted by such spurs.